Apparatus and method for forming a forward link transmission beam of a smart antenna in a mobile communication system

ABSTRACT

A method and apparatus for a base station including an antenna array calculates a direction of a weight vector of a transmission beam to maximize in-phase component power for a common channel signal in a transmission channel signal for transmission to a mobile station and to minimize a sum of quadrature-phase power component and interference power for other mobile stations inside and outside a cell due to a transmission channel signal for the mobile station.

PRIORITY

[0001] This application claims priority under 35 U.S.C. §119 to anapplication entitled “Apparatus and Method for Forming Forward LinkTransmission Beam of Smart Antenna in a Mobile Communication System”filed in the Korean Intellectual Property Office on May 17, 2002 andassigned Serial No. 2002-27324, the contents of which are incorporatedherein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to a smart antennaapparatus and method, and in particular, to an apparatus and method forforming forward link transmission beams of a smart antenna in a mobilecommunication system.

[0004] 2. Description of the Related Art

[0005] In order to meet a rapidly increasing demand for mobilecommunication and provide various multimedia services to users, there isa great necessity to increase capacity of a forward link. Typically,frequency division multiple access (FDMA) and time division multipleaccess (TDMA) are used to secure as large a subscriber capacity aspossible with the limited frequency bandwidth available. In FDMAtechnology, a given frequency bandwidth is divided into a plurality offrequency channels necessary for communication, so that subscribers eachuse unique frequency channels. However, in TDMA technology, eachsubscriber uses a single frequency channel only for a predetermined timeslot assigned thereto. Also, code division multiple access (CDMA) hasbeen proposed which uses the same frequency band but distinguishessubscribers by assigning different codes to the subscribers.

[0006] However, the method of increasing efficiency of a limitedfrequency band by these multiple access technologies has a limitation inaccommodating many subscribers. In order to overcome the limitation,cellular technology has been proposed. Cellular technology refers to amobile communication technology that divides a service area into aplurality of small regions, or cells, and uses the same frequency bandat two cells sufficiently distanced from each other to increase thenumber of spatially distributed channels, thereby securing sufficientsubscriber capacity. Moreover, it is possible to further increase basestation capacity by sectoring a base station antenna. For example, abase station antenna is sectored by changing an omnidirectional antennawith a 360° radiation pattern into three directional sector antennaswith a 120° radiation pattern. Particularly, in a CDMA system, if a basestation antenna is sectored, noises from subscribers of other sectorsare reduced, contributing to an increase in call capacity of the basestation.

[0007] Such conventional omnidirectional antenna or sector antennatransmits both a common channel signal and a transmission channel signalto a mobile station through a single common beam. The common channelsignal includes a pilot channel signal, a synchronization channel signaland a paging channel signal, all of which must be transmitted from abase station to all mobile stations in a corresponding cell. Thetransmission channel signal refers to a traffic channel signal that mustbe transmitted to a particular mobile station. A considerable amount ofradiation energy is wasted except the radiation energy transmitted to aparticular mobile station, e.g., when a particular signal such as thetransmission channel signal is transmitted to the particular mobilestation in the same manner as the common channel, rather than when apredetermined signal such as the common channel signal is transmittedfrom a base station's transmission antenna to all mobile stations. Inaddition, such radiation energy acts as an interference signal to othermobile stations except the corresponding mobile station.

[0008] Therefore, if it is possible to transmit a transmission channelsignal in a direction of a particular mobile station by certain means,it is possible to maintain high call quality while maintaining lowtransmission power and reducing interference signals to other mobilestations, thereby contributing to an increase in call capacity. Anantenna based on such a concept is an adaptive array antenna, also knownas an intelligent antenna or smart antenna.

[0009] A smart antenna system refers to an intelligent antenna systemwhich can automatically change its radiation beam pattern in response toa predetermined signal environment. The smart antenna system adopts atechnology for arranging a plurality of antenna elements in a specificform and multiplying an output of each antenna element by a complexweight, thereby forming an antenna beam in a direction of a desiredmobile station.

[0010] Such a smart antenna system is a technology that can be widelyused in a mobile communication field. Herein, however, the smart antennasystem will be described with reference to a CDMA cellular mobilecommunication system. In addition, the smart antenna system is atechnology in which a base station receives only a signal transmittedfrom a desired mobile station, in a reverse link, and concentratestransmission power only to a desired mobile station, on a forward link.Herein, the smart antenna system will be described on the assumptionthat a forward link transmission beam is formed.

[0011] A method for forming a forward link transmission beam of a smartantenna in a CDMA mobile communication system is disclosed in U.S. Pat.No. 6,108,565, which is incorporated herein by reference. The disclosedmethod calculates forward link transmission beam forming information byestimating an angle of arrival (AOA) and a time of arrival (TOA) fromsignals received at an antenna array of a base station from mobilestations. In addition, the patent discloses a method for forming aforward link transmission beam for each mobile station according to thecalculated AOA and TOA of a received signal. That is, a common channelsignal is transmitted through a wide beam, i.e., common beam, while atransmission channel signal for each mobile station is transmittedthrough a narrow beam, i.e., transmission beam, according to thecalculated forward link transmission beam forming information. Abeamwidth of the narrow beam is determined according to the distancebetween a mobile station and a base station. As the distance becomesshorter, the beamwidth becomes wider, while as the distance becomeslonger, the beamwidth becomes narrower. In addition, a beamwidth of thenarrow beam for the transmission channel signal is controlled accordingto a frame error rate (FER) reported over a reverse link.

[0012] A description of a method for forming a forward link transmissionbeam can be separately made with reference to one case where only acommon pilot channel is provided to all mobile stations in a cell andanother case where a dedicated pilot channel is provided to each mobilestation so that each mobile station can easily perform coherentdetection. In the latter case where the dedicated pilot channel isprovided, since the dedicated pilot channel and the transmission channeluse the same transmission beam, phase matching between both channels isguaranteed. However, in the former case where only the common pilotchannel is provided, since the common pilot channel and the transmissionchannel use different forward link transmission beams, phase mismatchingoccurs between both channels. The phase mismatching has a differentaftereffect according to a modulation scheme. Generally, a mobilecommunication system uses a modulation scheme of BPSK (Binary PhaseShift Keying) or QPSK (Quadrature Phase Shift Keying), commonly called“MPSK (Multiple Phase Shift Keying).” When the MPSK is used as amodulation scheme, a phase difference between a common channel signaland a transmission channel signal must be minimized in order to minimizea bit error rate (BER). That is, the phase mismatching must be minimizedto obtain desired call quality. Therefore, in a general mobilecommunication system, there is a necessity to minimize the phasemismatching.

[0013] In the CDMA mobile communication system, a signal from one useracts as an interference signal to another user, so the interference mustbe well controlled in order to increase channel capacity. In particular,as demand for data communication having higher power than voicecommunication has increased recently, the inference problem becomes moresignificant. The smart antenna system has been proposed to drasticallyreduce the interference signals by forming a forward link transmissionbeam so that a transmission channel signal is transmitted in a directionof a desired particular mobile station. Actually, however, a part of thetransmission channel signal transmitted to the desired mobile station isprovided to the other mobile stations inside and outside a cell, causingundesired interference. However, such inference is not considered in theforward link transmission beam forming method disclosed in the U.S. Pat.No. 6,108,565.

[0014] Meanwhile, if a beamwidth of a transmission beam is increased tobe as wide as a beamwidth of a common beam in order to minimize phasemismatching, interference to other mobile stations is increased. Incontrast, if the bandwidth of the transmission beam is decreased inorder to minimize interference, the phase mismatching is increased. Thatis, since the two conditions have a trade-off relation, it is necessaryto consider the two conditions together in order to form an optimaltransmission beam.

SUMMARY OF THE INVENTION

[0015] It is, therefore, an object of the present invention to providean apparatus and method for optimizing a forward link transmission beamby simultaneously considering an interference problem and a phasemismatching problem in a mobile communication system using a smartantenna.

[0016] It is another object of the present invention to provide anapparatus and method for calculating a direction of a weight vector of atransmission beam in order to maximize in-phase component power for acommon channel signal in a transmission channel signal for a mobilestation and to minimize the sum of quadrature-phase component power andinterference power for other mobile stations inside and outside a cell,caused by the transmission channel signal for the mobile station, in abase station apparatus including an antenna array.

[0017] It is further another object of the present invention to providean apparatus and method for calculating a direction of a weight vectorof a transmission beam so as to minimize interference power causedbecause a part of a transmission channel signal for a desired particularmobile station is flowed out to other mobile stations inside and outsidea cell when a dedicated pilot channel is provided, in a base stationapparatus including an antenna array.

[0018] It is yet another object of the present invention to provide anapparatus and method for independently calculating direction andmagnitude of a weight vector for a transmission beam for transmitting atransmission channel signal for a particular mobile station in a basestation apparatus including an antenna array.

[0019] It is still another object of the present invention to provide anapparatus and method for independently calculating weight vectors oftransmission beams for a plurality of mobile stations serviced by a basestation apparatus including an antenna array.

[0020] To achieve the above and other objects, there is provided atransmission beam forming control apparatus of a base station, forforming a transmission beam for a transmission channel signal to betransmitted to a mobile station from an antenna array including aplurality of antenna elements. A transmission beam weight vectorcalculator estimates a direction of the mobile station by using areception signal and a reverse link power control bit received from themobile station, and calculates a transmission beam weight vector in theestimated direction. A transmission beam former applies the calculatedtransmission beam weight vector to the transmission channel signal andproviding the applied transmission channel signal to the antenna array.

[0021] To achieve the above and other objects, there is provided atransmission beam forming control method of a base station, for forminga transmission beam for a transmission channel signal to be transmittedto a mobile station from an antenna array including a plurality ofantenna elements. The method comprises the steps of estimating adirection of the mobile station by using a reception signal and areverse link power control bit received from the mobile station, andcalculating a transmission beam weight vector in the estimateddirection; and applying the calculated transmission beam weight vectorto the transmission channel signal; and providing the appliedtransmission channel signal to the antenna array.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The above and other objects, features and advantages of thepresent invention will become more apparent from the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

[0023]FIG. 1 is a system diagram illustrating an example of a channelmodel of a forward link smart antenna according to an embodiment of thepresent invention;

[0024]FIG. 2 is a diagram illustrating an example of estimating reverselink transmission power according to an embodiment of the presentinvention;

[0025]FIG. 3 is a detailed block diagram illustrating an example ofcomponents of a base station transmission apparatus with an antennaarray according to an embodiment of the present invention;

[0026]FIG. 4 is a detailed block diagram illustrating an example ofcomponents of a transmission beam weight vector calculator according toan embodiment of the present invention;

[0027]FIG. 5 is a diagram illustrating an example of a transmission beamformer according to an embodiment of the present invention;

[0028]FIG. 6 is a graph illustrating a forward link transmission beampattern according to the prior art in terms of magnitude and degree; and

[0029]FIG. 7 is a graph illustrating a forward link transmission beampattern according an embodiment of the present invention in terms ofmagnitude and degree.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0030] Several embodiments of the present invention will now bedescribed in detail with reference to the accompanying drawings. In thedrawings, the same or similar elements are denoted by the same referencenumerals. In the following description, a detailed description of knownfunctions and configurations incorporated herein has been omitted forconciseness.

[0031] The embodiments of the present invention will be described withreference to two different cases. The first case provides a method forcalculating an optimal transmission weight vector when there is nodedicated pilot channel and only a common pilot channel exists. Thesecond case provides a method for calculating an optimal transmissionweight vector when a dedicated pilot channel exists, e.g., the specialcase described in conjunction with the prior art. Embodiments of thepresent invention can be generally applied to a current mobilecommunication system, such as FDMA, TDMA and CDMA. However, forconvenience, the embodiments of the present invention will be describedwith reference to a CDMA system, especially a 3^(rd) generation CDMAmobile communication system such as a CDMA2000 system and a WCDMA(Wideband CDMA) system. Meanwhile, it will be assumed herein thatdirection and magnitude of a weight vector for a common beam werepreviously calculated by known means.

[0032]FIG. 1 is a system diagram illustrating an example of a channelmodel of a forward link smart antenna according to an embodiment of thepresent invention. Specifically, FIG. 1 illustrates a channel model of aforward link smart antenna on the assumption that M mobile stationsMS_(i) (i=1,2, . . . ,M) in a cell are communicating with a base stationBS. In FIG. 1, s_(m) (t) represents a forward link traffic channelsignal for an m^(th) mobile station MS from a base station BS, h_(m)represents a forward link channel response vector from the base stationBS to an m^(th) mobile station MS_(m), and w_(m) represents a forwardlink weight vector from the base station BS to an m^(th) mobile stationMS_(m). In addition, channel response vectors from the base station BSto a plurality of mobile stations located in other cells are representedby h_(oc).

[0033] If a forward link signal transmitted from the base station BS tomobile stations via an antenna array comprised of a plurality of antennaelements is defined as s(t), the s(t) becomes a linear combination of acommon channel signal s_(p)(t) with a common weight vector w_(p) and atraffic channel signal s_(i)(t)(i=1,2, . . . ,M) with an individualtransmission weight vector w_(i)(i=1,2, . . . , M). That is, the s(t)can be represented by $\begin{matrix}{{\underset{\_}{s}(t)} = {{{\underset{\_}{w}}_{p}{{\underset{\_}{s}}_{p}(t)}} + {\sum\limits_{i = 1}^{M}{{\underset{\_}{w}}_{i}{s_{i}(t)}}}}} & {{Equation}\quad (1)}\end{matrix}$

[0034] Although the common channel signal includes a pilot channelsignal, a synchronization channel signal and a paging channel signal,only the pilot channel signal will be designated herein as the commonchannel signal, for the convenience of explanation. The pilot channelsignal s_(p)(t) is a signal transmitted over an omidirectional beam or asector beam in order to provide time and phase criteria for coherentdemodulation to mobile stations in a cell. Therefore, a weight vectorw_(p) for the pilot channel signal should be able to entirely cover theinside of a cell or the inside of a sector. In the present examples, itis assumed that the w_(p) is previously calculated through known means.What is provided is a method for calculating transmission weight vectorsw_(i)(i=1,2, . . . ,M) for traffic channel signals s_(i)(t)(i=1,2, . . .,M) transmitted to each of the mobile stations in the cell, by anoptimal criterion. For convenience, the description will be limited to amethod for calculating a transmission weight vector w_(m) for an m^(th)mobile station MS_(m) among M mobile stations. Of course, transmissionweight vectors for the other mobile stations can also be calculated inthe same method. Therefore, it is possible to independently calculatetransmission weight vectors for the respective mobile stations.

[0035] When a base station transmits a signal s(t) over a radio channel,a signal r_(m)(t) received at an m^(th) mobile station MS_(m) can berepresented by $\begin{matrix}\begin{matrix}{{r_{m}(t)} = {{\underset{\_}{s}(t)}^{H}{\underset{\_}{h}}_{m}}} \\{= {{{\underset{\_}{w}}_{p}^{H}{\underset{\_}{h}}_{m}{s_{p}^{*}(t)}} + {\sum\limits_{i = 1}^{M}{{\underset{\_}{w}}_{i}^{H}{\underset{\_}{h}}_{m}{s_{i}^{*}(t)}}}}}\end{matrix} & {{Equation}\quad (2)}\end{matrix}$

[0036] In Equation (2), * denotes a conjugate operator, and H denotes aHermitian operator.

[0037] The signal r_(m)(t) is divided into a pilot channel signalr_(p)(t), a traffic channel signal r_(d)(t) for an m^(th) mobile stationMS_(m), and an interference signal r_(imp)(t) indicating a signaltransmitted to other mobile stations but flowed into or provided to anm^(th) mobile station MS_(m), as illustrated in Equation (3).$\begin{matrix}\begin{matrix}{{r_{p}(t)} = {{\underset{\_}{w}}_{p}^{H}{\underset{\_}{h}}_{m}{s_{p}^{*}(t)}}} \\{{r_{d}(t)} = {{\underset{\_}{w}}_{m}^{H}{\underset{\_}{h}}_{m}{s_{m}^{*}(t)}}} \\{{r_{imp}(t)} = {\underset{i \neq m}{\sum\limits_{i = 1}^{M}}{{\underset{\_}{w}}_{i}^{H}{\underset{\_}{h}}_{m}{s_{i}^{*}(t)}}}}\end{matrix} & {{Equation}\quad (3)}\end{matrix}$

[0038] Power of each signal received at an m^(th) mobile station MS_(m)shown in Equation (3) can be expressed by Equation (4) below. InEquation (4), P_(p) represents power of a pilot channel signal, P_(d)represents power of a traffic channel signal, and P_(imp) representspower of an interference signal. $\begin{matrix}\begin{matrix}{P_{p} = {{\underset{\_}{w}}_{p}^{H}R_{m}S_{p}{\underset{\_}{w}}_{p}}} \\{P_{d} = {{\underset{\_}{w}}_{m}^{H}R_{m}S_{m}{\underset{\_}{w}}_{m}}} \\{P_{imp} = {\underset{i \neq m}{\sum\limits_{i = 1}^{M}}{{\underset{\_}{w}}_{i}^{H}R_{m}S_{i}{\underset{\_}{w}}_{i}}}}\end{matrix} & {{Equation}\quad (4)}\end{matrix}$

[0039] In Equation (4), R_(m) represents a forward link transmissioncovariance matrix for an m^(th) mobile station MS_(m) and isR_(m)=[h_(m)h_(m) ^(H)], and S_(p) represents power of a pilot channelsignal transmitted from a base station and is S_(p)=E[|s_(i)(f)|²]. Inaddition, S_(i) represents power of a forward link traffic channelsignal transmitted from a base station to an i^(th) mobile stationMS_(i) and is S_(i)=E[|s_(i)(f)|²], and S_(m) represents power of aforward link traffic channel signal transmitted to an m^(th) mobilestation MS_(m).

[0040] When there is no dedicated pilot channel and only a common pilotchannel exists, a weight vector w_(p) applied to a common pilot channelis generally different from a weight vector w_(m) applied to a trafficchannel, thus causing phase mismatching between a pilot channel signaland a traffic channel signal received at an m^(th) mobile stationMS_(m), illustrated in Equation (3). Here, phase variation due tos_(p)(t) and s_(m)(t) of the signal is excluded.

[0041] However, since a traffic channel is synchronized by a pilotchannel, a common pilot channel signal becomes a phase criterion in amobile station. Therefore, of the traffic channel signal of Equation(3), a component phase-matched to the pilot channel signal acts as asignal component, while a component phase-mismatched to the pilotchannel signal acts as an interference component. Herein, the componentphase-matched to the pilot channel signal is referred to as “in-phasecomponent,” and the component phase-mismatched to the pilot channelsignal is referred to as “quadrature-phase component.” Considering this,the traffic signal power P_(d) of Equation (4) can be divided intoin-phase power P_(i) and quadrature-phase power P_(q), as shown inEquation (5) below. $\begin{matrix}\begin{matrix}{P_{i} = {{{\underset{\_}{w}}_{m}^{H}R_{m}S_{m}{\underset{\_}{w}}_{p}^{\prime}}}^{2}} \\{P_{q} = {{\underset{\_}{w}}_{m}^{H}R_{m}S_{m}{\underset{\_}{w}}_{p}^{-}{{{\underset{\_}{w}}_{m}^{H}R_{m}S_{m}{\underset{\_}{w}}_{p}^{\prime}}}^{2}}}\end{matrix} & {{Equation}\quad (5)}\end{matrix}$

[0042] In Equation (5), w′_(p) is${\underset{\_}{w}}_{p}^{\prime} = {{\underset{\_}{w}}_{p}/\sqrt{{\underset{\_}{w}}_{p}^{H}R_{m}S_{m}{\underset{\_}{w}}_{p}}}$

[0043] and represents a normalized weight vector of a pilot channel.

[0044] Meanwhile, of the s(t) transmitted from the base station BS, aninterference signal r_(exp)(t) indicating a traffic channel signal${\underset{\_}{w}}_{m}^{H}{s_{m}^{*}(t)}$

[0045] to be transmitted only to an mobile station MS_(m) but flowed outto other mobile stations MS_(i) (i=1,2, . . . ,M) in a cell, and aninterference signal r_(oc)(t) indicating the traffic channel signalflowed out to mobile stations belonging to other cells can berepresented by $\begin{matrix}\begin{matrix}{{r_{\exp}(t)} = {\underset{i \neq m}{\sum\limits_{i = 1}^{M}}{{\underset{\_}{w}}_{m}^{H}{\underset{\_}{h}}_{i}{s_{m}^{*}(t)}}}} \\{{r_{oc}(t)} = {{\underset{\_}{w}}_{m}^{H}{\underset{\_}{h}}_{oc}{s_{m}^{*}(t)}}}\end{matrix} & {{Equation}\quad (6)}\end{matrix}$

[0046] Power of the inference signals due to outflow of a signal toother mobile stations inside and outside the cell can be defined as$\begin{matrix}\begin{matrix}{P_{\exp} = {\underset{i \neq m}{\sum\limits_{i = 1}^{M}}{{\underset{\_}{w}}_{m}^{H}R_{i}S_{m}{\underset{\_}{w}}_{m}}}} \\{P_{oc} = {{\underset{\_}{w}}_{m}^{H}R_{oc}S_{m}{\underset{\_}{w}}_{m}}}\end{matrix} & {{Equation}\quad (7)}\end{matrix}$

[0047] In Equation (7), R_(oc), denotes a forward link transmissioncovariance matrix for mobile stations within other cells, and can berepresented by$R_{oc} = {{E\left\lbrack {{\underset{\_}{h}}_{oc}{\underset{\_}{h}}_{oc}^{H}} \right\rbrack}.}$

[0048] In addition, a thermal noise generated within a mobile stationcan be considered together with interference signals from other mobilestations, and the thermal noise can be given by

P_(th)=σ_(th) ²  Equation (8)

[0049] A weight vector for a transmission beam is calculated using theenumerated signal and interference power. First, in order to calculate adirection of a weight vector for a transmission beam for an m^(th)mobile station MS_(m), a signal-to-inference plus noise ratio (SINR) forforward link beam forming (FLBF) is defined as $\begin{matrix}{{SINR}_{m}^{FLBF} = {\frac{P_{i}}{P_{q} + P_{\exp} + P_{oc}} = \frac{\left| {{\underset{\_}{w}}_{m}^{H}R_{m}S_{m}{\underset{\_}{w}}_{p}^{\prime}} \right|^{2}}{\left( \left. {{\underset{\_}{w}}_{m}^{H}R_{m}S_{m}{\underset{\_}{w}}_{m^{-}}} \middle| {{\underset{\_}{w}}_{m}^{H}R_{m}S_{m}{\underset{\_}{w}}_{p}^{\prime}} \right|^{2} \right) + {\underset{i \neq m}{\sum\limits_{i = 1}^{M}}{{\underset{\_}{w}}_{m}^{H}R_{i}S_{m}{\underset{\_}{w}}_{m}}} + {{\underset{\_}{w}}_{m}^{H}R_{oc}S_{m}{\underset{\_}{w}}_{m}}}}} & {{Equation}\quad (9)}\end{matrix}$

[0050] The SINR_(m)^(FLBF)

[0051] is not a value that can be actually measured in a correspondingmobile station MS_(m). However, in order to maximize the SINR_(m)^(FLBF)

[0052] in Equation (9), it is necessary to minimize the sum of aquadrature-phase component power P_(q) and interference powers P_(exp)and P_(oc) indicating a signal transmitted to a corresponding mobilestation MS_(m) but flowed out to other mobile stations inside andoutside a cell while maximizing in-phase component power P_(i), for aphase of a pilot channel signal serving as a phase criterion duringcoherent detection. As a result, from the viewpoint of the overallsystem, actual SINR_(m)^(FLBF)

[0053] is increased in a mobile station MS_(m). Therefore, it ispossible to define the SINR of Equation (9) instead of using the actualSINR_(m)^(FLBF).

[0054] If a transmission beam weight vector w_(m) for maximizingSINR_(m)^(FLBF)

[0055] is calculated through the definition, the calculated valuebecomes an optimal weight vector ${\underset{\_}{w}}_{m}^{opt}$

[0056] for minimizing phase mismatching between a pilot channel signaland a traffic channel signal and also minimizing power of aninterference signal for other mobile stations, thereby achieving objectsof the present invention.

[0057] In addition, the SINR_(m)^(FLBF)

[0058] becomes a function of only a transmission beam weight vectorw_(m) for an m^(th) mobile station MS_(m) when a common beam weightvector w_(p) is given. As a result, it is possible to independentlyoptimize the transmission beam weight vector according to mobilestations. Particularly, it can be understood from Equation (9) thatSINR_(m)^(FLBF)

[0059] depends upon only a direction of a forward link channel responsevector w_(m) regardless of magnitude of a forward link channel responsevector w_(m) from a base station to a corresponding mobile station and aforward link traffic channel signal S_(m) for the corresponding mobilestation. From this, it can be noted that it is possible to independentlycalculate direction and magnitude of the forward link channel responsevector w_(m).

[0060] In Equation (9), a calculation result obtained by selecting theoptimal forward link weight vector ${\underset{\_}{w}}_{m}^{opt}$

[0061] as a value for maximizing SINR_(m)^(FLBF)

[0062] becomes $\begin{matrix}\begin{matrix}{{\underset{\_}{w}}_{m}^{\prime} = {\underset{{\underset{\_}{w}}_{m}}{Maximize}\quad {SINR}_{m}^{FLBP}}} \\{= {\left( {{\sum\limits_{i = 1}^{M}R_{i}} + R_{oc}} \right)^{- 1}R_{m}{\underset{\_}{w}}_{p}}} \\{\gamma_{m} = {{\underset{\_}{w}}_{m}^{\prime \quad H}R_{m}{\underset{\_}{w}}_{p}}} \\{{\underset{\_}{w}}_{m}^{opt} = {\gamma_{m}{\underset{\_}{w}}_{m}^{\prime}}}\end{matrix} & {{Equation}\quad (10)}\end{matrix}$

[0063] For covariance matrixes used in Equation (10), other means, forexample, a forward link covariance matrix fed back from a mobile stationMS_(m) to a base station BS or its equivalent information can be used.When there is no information fed back from the mobile station to thebase station, the base station can estimate signals received from mobilestations. A detailed description of this will be made later. A signalγ_(m) received from an m^(th) mobile station MS_(m) was introduced tocalculate w_(m) for maximizing SINR_(m)^(FLBF)

[0064] and then additionally control a phase between a common beam and atransmission beam.

[0065] A description has been made of a method for calculating anoptimal weight vector when there is no dedicated pilot channel and onlya common pilot channel exists. However, when a dedicated pilot channelexists, a weight vector for the dedicated pilot channel serving as aphase criterion during coherent detection is identical in phase to aweight vector applied to a traffic channel. Therefore, if a dedicatedpilot channel exists, a phase mismatching problem between the dedicatedpilot channel and the traffic channel does no occur. Thus, Equation (5)can be written as

P _(i) =P _(d) =w _(m) ^(H) R _(m) S _(m) w _(m)  Equation (11)

P_(q)=0

[0066] Therefore, SINR_(m)^(FLBF)

[0067] for forward link beam forming is defined as $\begin{matrix}{{SINR}_{m}^{FLBF} = \frac{{\underset{\_}{w}}_{m}^{H}R_{m}S_{m}{\underset{\_}{w}}_{m}}{{\sum\limits_{\underset{i \neq m}{i = 1}}^{M}\quad {{\underset{\_}{w}}_{m}^{H}R_{i}S_{m}{\underset{\_}{w}}_{m}}} + {{\underset{\_}{w}}_{m}^{H}R_{oc}S_{m}{\underset{\_}{w}}_{m}}}} & \text{Equation~~(12)}\end{matrix}$

[0068] When the dedicated pilot channel exists, an optimal weight vectorfor a traffic channel represents a value for maximizing $\begin{matrix}{{\underset{\_}{w}}_{m}^{opt} = {{Principal}\quad {Eigenvector}\quad {{of}\left( {{\sum\limits_{i = 1}^{M}R_{i}} + R_{oc}} \right)}^{- 1}R_{m}}} & \text{Equation~~(13)}\end{matrix}$

[0069] Of Equation (12) and is calculated by SINR_(m)^(FLBF)

[0070] As described above, for forward link beam forming according topresence/absence of the dedicated pilot channel, forward linktransmission covariance matrixes R_(m)(m=1,2, . . . ,M) and R_(oc), i.e.R_(m)^(FL)(m = 1, 2, …  , M)

[0071] and R_(oc)^(FL),

[0072] are required as illustrated in Equation (13). So far, a reverselink (RL) related signal and a forward link (FL) related signal have notbeen distinguished for purposes of simplicity, since they may not beconfused. However, henceforth, a superscription ‘FL’ will be used for aforward link and a superscription ‘RL’ will be used for a reverse link,for signal distinguishment. As stated above, if such information isprovided from a mobile station, the information can be used as it is. Incontrast, if the information is not provided, a base station mustestimate a forward link covariance matrix from a signal received from amobile station. However, since a reverse link covariance matrixR_(m)^(RL)S_(m)^(RL)

[0073] is obtained from the received reverse link signal, the basestation is required to first estimate transmission power S_(m)^(RL)

[0074] of a mobile station MS_(m) and to eliminate the estimatedtransmission power.

[0075] In the current mobile communication standard, a base station BShas no way to directly receive transmission power S_(m)^(RL)

[0076] of a mobile station MS_(m). Instead, the base station BS canindirectly estimate transmission power S_(m)^(RL)

[0077] of a mobile station MS_(m), using a reverse power control bittransmitted to the mobile station MS_(m) every slot for reverse linkpower control.

[0078]FIG. 2 is a diagram illustrating an example of estimating reverselink transmission power according to an embodiment of the presentinvention. Specifically, FIG. 2 illustrates an example of estimatingtransmission power S_(m)^(RL)

[0079] of a mobile station MS_(m) from a reverse link power control bit.In FIG. 2, PCB_(m)^(RL)(t_(k))

[0080] means a reverse link power control bit that a base station BStransmits to an m^(th) mobile station MS_(m) every slot f_(k)(k=1,2, . .. ) As illustrated in FIG. 2, transmission power of a mobile station isincreased or decreased in a predetermined ratio according toPCB_(m)^(RL)(t_(k)).

[0081] The transmission power S_(m)^(RL)(t_(k))

[0082] of a mobile station is calculated by $\begin{matrix}{{S_{m}^{RL}\left( t_{k} \right)} = {S_{0} \cdot 10^{\frac{{Increment}\quad \times {\sum\limits_{j = 1}^{k}\quad {{PCB}_{m}^{RL}{(t_{j})}}}}{10}}}} & \text{Equation~~~(14)}\end{matrix}$

[0083] In Equation (14), ‘Increment’ represents a transmission powerratio (dB) that increases or decreases according to a reverse link powercontrol bit, and S_(o) represents initial transmission power. Equation(14) provides a value that the base station BS can calculate, andthrough this, the base station can estimate transmission power of amobile station. Equation (14) is given on the assumption that no erroroccurs during transmission and demodulation of the reverse link powercontrol bit. However, even when an error occurs during transmission ofthe reverse link power control bit, an actual value can be immediatelyrecovered through feedback of the reverse link power control bit.

[0084] When power S_(m)^(RL)

[0085] of a reverse link traffic channel received from an m^(th) mobilestation is estimated, a transmission covariance matrix R_(m)^(RL)

[0086] for a reverse link channel from the m^(th) mobile station can becalculated from the estimated power. In addition, AOA and beamwidth areestimated from the transmission covariance matrix R_(m)^(RL)

[0087] for a reverse link channel received from the m^(th) mobilestation. Further, a transmission covariance matrix R_(m)^(FL)

[0088] for a forward link channel to an m^(th) mobile station can beestimated by synthesizing a covariance matrix considering a differencebetween transmission and reception frequency bands from the estimatedAOA and beamwidth.

[0089] Even for a transmission covariance matrix R_(oc) for mobilestations in other cells, a similar method can be used. However, it canbe difficult to individually detect transmission power of mobilestations inside and outside a cell. In this case, it is necessary topreviously determine expected average values of a transmissioncovariance matrix R_(oc) for mobile stations inside and outside othercells. Generally, since it is assumed that interference from other cellsis spatially uniform, the expected average value can be applied withoutany problem.

[0090] A description has been made of a method of simultaneouslyconsidering a phase mismatching problem between a common pilot channelsignal and a traffic channel signal and an interference problem forother mobile stations when a dedicated pilot channel is not provided.Another method of calculating a direction of an optimal transmissionbeam weight vector through forward link beam forming considering aninterference problem when the dedicated pilot channel is provided. Fromnow on, a description will be made of a process of calculating magnitudeof a transmission beam weight vector using forward link power control(FLPC).

[0091] Equation (15) shows an example of SINR_(m)^(FLPC)

[0092] for forward link power control on an m^(th) mobile station MS_(m)in a cell. $\begin{matrix}{{SINR}_{m}^{FLPC} = \frac{P_{i}}{P_{q} + P_{imp} + P_{p} + P_{th}}} & {\text{Equation~~}(15)}\end{matrix}$

[0093] The SINR_(m)^(FLPC)

[0094] is a value that can directly measured by an m^(th) mobile stationMS_(m). The SINR_(m)^(FLPC)

[0095] for forward link power control can be defined differentlyaccording to systems. In the present example, since a forward link powercontrol function provided in an existing CDMA system will be applied asis, a detailed definition of SINR_(m)^(FLPC)

[0096] is not important.

[0097] An m^(th) mobile station MS_(m) compares a target value of theSINR_(m)^(FLPC)

[0098] with its current bit measured value, and determines a forwardlink power control bit PCB_(m)^(FL)

[0099] according to the comparison result. A base station BS receivesthe forward link power control bit PCB_(m)^(FL)

[0100] over a reverse link channel, and determines signal powerS_(m)^(FL)

[0101] of a forward traffic channel, i.e., magnitude of a weight vectorfor a transmission beam, according to a value of the received forwardlink power control bit.

[0102] By calculating a direction of an optimal weight vector of eachmobile station through forward link beam forming and independentlycalculating desired base station transmission power through forward linkpower control, a smart antenna adopting a forward link beam formingalgorithm proposed herein can achieve a desired SINR with minimum basestation transmission power, as compared with an omnidirectional antennaor a sector antenna. Thus, it is possible to increase the number ofavailable mobile stations in a cell, contributing to an increase insubscriber capacity, an object of the smart antenna.

[0103] A detailed description will now be made of an embodiment of thepresent invention with reference to the accompanying drawings.

[0104]FIG. 3 is a detailed block diagram illustrating an example ofcomponents of a base station transmission apparatus with an antennaarray according to an embodiment of the present invention. Asillustrated, the transmission apparatus for a base station includes anantenna array 300, an RF (Radio Frequency) part 310, a transmission beamformer 320, a transmission beam controller 330, a common channel signalgenerator 340, a transmission channel signal generator 350, a receptionbeam former 360, and a base station modem receiver 370. It is assumedthat the base station is currently communicating with M mobile stationsin the cell.

[0105] It is assumed that the antenna array 300 is comprised of Nidentical antenna elements. An antenna array can be classified into atransmission antenna array and a reception antenna array. Here, adescription will be made with reference to the transmission antennaarray. However, a hardware structure of the antenna array is commonlydesigned such that it can be jointly used for both transmission andreception by use of a duplexer. The antenna array 300 transmitstransmission beams formed by the transmission beam former 320, andprovides RF signals received from several mobile stations inside andoutside a cell to the RF part 310.

[0106] The RF part 310 is comprised of N RF units corresponding to the Nantenna elements of the antenna array 300, and each RF unit is connectedto its associated antenna element. Each RF unit, though not illustrated,includes a low-noise amplifier, a frequency down converter, and ananalog-to-digital (A/D) converter. The RF part 310 converts RF signalsreceived from mobile stations via the antenna array 300 into a basebanddigital reception signal x.

[0107] The reception beam former 360 converts the baseband digitalreception signal x output from the RF part 310 into beams z_(i)(i=1,2, .. . ,M) formed as to mobile stations, and provides the output beams tothe base station modem receiver 370. The reception beam former 360serves as a spatial filter capable of amplifying or eliminating a signalbased on a direction of a signal received from each mobile station viathe antenna array 300. When a RAKE receiver, not shown for purposes ofsimplicity, is used to eliminate an interference signal due to multipathfading, the reception beam former 360 can be positioned before or aftera demodulator in each finger of the RAKE receiver.

[0108] The base station modem receiver 370 modulates the beamsz_(i)(i=1,2, . . . ,M) output from the reception beam former 360 intovoice or data signals of corresponding mobile stations. In addition, thebase station modem receiver 370 restores forward link power control bitsPCB_(i)^(FL)(i = 1, 2, …  , M)

[0109] transmitted from corresponding mobile stations and measures SINRfor the corresponding mobile stations, thereby determining reverse linkpower control bits PCB_(i)^(RL)(i = 1, 2, …  , M).

[0110] Moreover, the base station modem receiver 370 restores a forwardlink FER transmitted from a corresponding mobile station by help of anupper layer.

[0111] The transmission beam controller 330 calculates weight vectorsfor controlling forming of transmission beams, and includes a commonbeam weight vector calculator 331, a transmission beam weight vectorcalculator 333, a common beam power calculator 335 and a transmissionbeam power calculator 337. In embodiments of the present invention, thecalculators can be optionally implemented by hardware or software.

[0112] The transmission beam former 320 includes a common beam former323 for forming a common beam, M transmission beam formers 325 forforming transmission beams for M mobile stations, and N adders 321 forforming M forward transmission beams by adding the common beam to the Mtransmission beams, and then providing the formed forward transmissionbeams to the N RF units corresponding thereto.

[0113] A detailed description will now be made of an operation offorming transmission beams by a base station having the structure statedabove.

[0114] RF signals received from several mobile stations inside andoutside the cell through N antenna elements of the antenna array 300 areconverted into baseband digital reception signal x by the RF part 310,and then provided to the reception beam former 360 and the transmissionbeam weight vector calculator 333. The transmission beam weight vectorcalculator 333 calculates forward link transmission covariance matrixesR_(i)^(FL)(i = 1, 2, …  , M)

[0115] in the above-stated method by receiving the baseband digitalreception signal x from the RF part 310 and the reverse link powercontrol bits PCB_(i)^(RL)(i = 1, 2, …  , M)

[0116] from the base station modem receiver 370. When a dedicated pilotchannel is not provided, the forward link transmission covariance matrixis calculated using Equation (10) above. In contrast, when the dedicatedpilot channel is provided, the forward link transmission covariancematrix is calculated using Equation (13) above. Therefore, thetransmission beam weight vector calculator 333 can be designed toinclude both of the two calculation methods so that it can optionallyuse one of the two calculation methods. In an embodiment of the presentinvention, the transmission beam weight vector calculator 333 can bedesigned to include only a calculation method corresponding to aparticular system. In this method, the transmission beam weight vectorcalculator 333 calculates optimal transmission beam weight vectorsw_(i)(i=1,2, . . . ,M) for the mobile stations on a real-time basis, andprovides the optimal transmission beam weight vectors to thecorresponding transmission beam formers 325.

[0117] The transmission beam power calculator 337 calculatestransmission beam powers S_(i)(i=1,2, . . . ,M) for the mobile stationsby receiving the forward link power control bitsPCB_(i)^(FL)(i = 1, 2, …  , M)

[0118] from the base station modem receiver 370, and provides thecalculated transmission beam powers to the transmission channel signalgenerators 350. Each transmission channel signal generator 350 generatestransmission channel signals s_(i)(i=1,2, M) by multiplying thetransmission channel signals having a unit magnitude by square roots ofthe transmission beam powers S_(i)(i=1,2, . . . ,M), and provides thegenerated transmission channel signals to the corresponding transmissionbeam former 325.

[0119] The transmission beam formers 325 form transmission beams bymultiplying optimal transmission beam vectors w_(i)(i=1,2, . . . ,M) forthe mobile stations by the transmission channel signals s_(i)(i=1,2, . .. ,M). The transmission beams formed in this manner are provided to theadders 321 associated with the N antenna elements of the antenna array300.

[0120] A weight vector for a common beam is determined by the commonbeam weight vector calculator 331 and the common beam power calculator335. The common beam weight vector calculator 331 previously calculatesa common beam weight vector w_(p) capable of covering a cell or asector, and provides the calculated common beam weight vector to thecommon beam former 323. Meanwhile, the common beam power calculator 335previously calculates common beam power S_(p), and provides thecalculated common beam power to the common channel signal generator 340.The common channel signal generator 340 generates a common channelsignal s_(p) by multiplying a common channel signal having a unitmagnitude by a square root of the common beam power S_(p), and providesthe generated common channel signal to the common beam former 323.

[0121] The common beam former 323 multiplies the common channel signals_(p) by the common beam weight vector w_(p), and provides its output tothe adders 321 associated with the N antenna elements of the antennaarray 300.

[0122] The adders 321 form base station transmission signal vectors s(t)by summing up outputs of the common beam former 323 and the transmissionbeam formers 325, and provide their outputs to the corresponding RFunits of the RF part 310. The transmission signal vectors s(t) from thebase station to the mobile stations are converted into RF signals by theRF units 310 after being power-amplified through a D/A converter, afrequency up converter and a power amplifier, and then transmitted tothe mobile stations in the cell over forward link channels through theantenna array 300.

[0123]FIG. 4 is a detailed block diagram illustrating an example ofcomponents of the transmission beam weight vector calculator 333 shownin FIG. 3. Specifically, FIG. 4 illustrates an apparatus and method forestimating forward link covariance matrixes for M mobile stationsMS_(i)(i=1,2, . . . ,M) from a reverse link base station receptionsignal vector x. Although the forward link covariance matrix can beestimated from the reverse link base station reception signal vector asmentioned above, it can also be directly fed back from the mobilestations or can be calculated using other methods. In addition, itshould be appreciated by those skilled in the art that although thetransmission beam weight vector calculator 333 is realized by hardwarein FIG. 4, it can also be implemented by software without departing fromthe scope of the present invention.

[0124] Referring to FIG. 4, the transmission beam weight vectorcalculator 333 includes M forward link covariance matrix calculators 400associated with M mobile stations MS_(i)(i=1,2, . . . ,M), M optimalweight vector calculators 420, and an other cell covariance matrixcalculator 410. Each forward link covariance matrix calculator 400 iscomprised of a reverse link covariance matrix estimator 401, an AOAestimator 403, a beamwidth estimator 405, and a forward link covariancematrix synthesizer 407.

[0125] The reverse link covariance matrix estimator 401 first calculatesa covariance matrix R_(i)^(RL)S_(i)^(RL)

[0126] for an i^(th) mobile station MS_(i) by receiving the basebanddigital reception signal vector x. Further, the reverse link covariancematrix estimator 401 estimates mobile station transmission powerS_(i)^(RL)

[0127] using a reverse link power control bit PCB_(i)^(RL),

[0128] and then calculates a reverse link transmission covariance matrixR_(i)^(RL)

[0129] of an i^(th) mobile station from the estimated mobile stationtransmission power. The reverse link covariance matrix estimator 401provides the calculated reverse link covariance matrix to the AOAestimator 403 and the beamwidth estimator 405. The AOA estimator 403 andthe beamwidth estimator 405 calculate an AOA estimation value AOA_(i)and a beamwidth estimation value BW_(i) for a corresponding mobilestation from the reverse link covariance matrix estimation valueR_(i)^(RL),

[0130] and provide the calculated AOA_(i) and BW_(i) to the forward linkcovariance matrix synthesizer 407. In an abnormal state where FER isincreased abruptly for some reason, the beamwidth estimator 405 detectsthe abrupt increase in the FER from a forward link FER_(i)^(FL)

[0131] received from a mobile station and then increases or decreasesthe beamwidth by a predetermined value, thereby appropriately copingwith the abnormal state.

[0132] The forward link covariance matrix synthesizer 407 synthesizes aforward link covariance matrix estimation value R_(i)^(FL)

[0133] from the AOA estimation value AOA_(i) and the beamwidthestimation value BW_(i), and provides the synthesized forward linkcovariance matrix estimation value to the optimal weight vectorcalculator 420. In an FDD (Frequency Division Duplexing) system where atransmission frequency band is different from a reception frequencyband, a difference between the transmission frequency and the receptionfrequency is compensated for in the forward link covariance matrixsynthesizer 407.

[0134] The other cell covariance matrix calculator 410 calculates acovariance matrix estimation value R_(oc) for interference to mobilestations in other cells due to a transmission channel signal for ani^(th) mobile station MS_(i), by receiving the baseband digitalreception signal vector x, and providing the calculated covariancematrix estimation value to the optimal weight vector calculator 420.Estimation of the reverse link covariance matrix and the other cellcovariance matrix can be performed using a known technique. For example,a method disclosed in “Performance Analysis of CDMA Mobile CommunicationSystems using Antenna Arrays”, B. Suard, A. Naguib, G, Xu, A. Paulraj,Proc. ICASSP, 1993, which is incorporated herein by reference, can beused.

[0135] The optimal weight vector calculator 420 calculates an optimalweight vector w_(i) in accordance with Equation (10) or Equation (11) byreceiving a forward link covariance matrix estimation value R_(i) for ani^(th) mobile station MS_(i) from the forward link covariance matrixcalculator 400, an estimation value R_(oc) from the other cellcovariance matrix calculator 410, and a common beam weight vector w_(p)from the common beam weight vector calculator 331, and then provides thecalculated optimal weight vector to the transmission beam former 325.

[0136]FIG. 5 is a diagram illustrating an example of the transmissionbeam former 325 for an m^(th) mobile station MS_(m) according to anembodiment of the present invention. If it is assumed that the antennaarray of the base station includes N antenna elements, the transmissionbeam former 325 includes N complex multipliers 510 associated with theantenna elements. A transmission beam weight vector w_(m) for an m^(th)mobile station MS_(m) is divided into N elements associated with theantenna elements, and then applied to the corresponding complexmultipliers 510. It is well known that the w_(m) can be represented byw_(m)=[w_(m,1)w_(m,2) . . . w_(m,N−1)w_(m,N)]^(T). The complexmultipliers 510 complex-multiply a traffic channel signal s_(m)(f) foran m^(th) mobile station MS_(m) by the elements of the weight vectorw_(m), and provide their outputs to the corresponding adders 321.

[0137] Although the transmission beam former 325 for an m^(th) mobilestation MS_(m) is illustrated in FIG. 5, transmission beam formers forother mobile stations also have the same structure. Also, common beamformers for other mobile stations have the same structure as the commonbeam former 323.

[0138]FIG. 6 is a graph illustrating a forward link transmission beampattern according to the prior art in terms of magnitude and degree, andFIG. 7 is a graph illustrating a forward link transmission beam patternaccording to an embodiment of the present invention in terms ofmagnitude and degree. FIGS. 6 and 7 are based on the assumption that thenumber of forward link transmission beams is 2 in a base station'slinear antenna array that has 4 antenna elements and a gap between theantenna elements is half a wavelength. Specifically, FIG. 6 illustratesa forward link transmission beam pattern formed by considering only AOAand beamwidth from a signal received at the base station from the mobilestation, and FIG. 7 illustrates a forward link transmission beam patternformed according to an embodiment of the present invention. It isfurther assumed in FIGS. 6 and 7 that forward link transmission beams610 and 710 shown by solid lines are for AOA=−40° and beamwidth=20°, andforward link transmission beams 620 and 720 also shown by solid linesare for AOA=−0° and beamwidth=20°.

[0139] It can be understood that compared with the forward linktransmission beam pattern illustrated in FIG. 6, the forward linktransmission beam pattern illustrated in FIG. 7 has interference reducedby about 3 to 4 dB within a non-transmission angle range. That is, whena forward link transmission beam is formed according to the disclosedembodiments of the present invention, it is possible to increase theamount of subscriber capacity by the same amount as the reduction in theinterference signal.

[0140] As described above, the disclosed embodiments of the presentinvention can form an optimal transmission beam for minimizing phasemismatching between a common beam and a transmission beam and alsominimize interference to other mobile stations due to the transmissionbeam. That is, the invention can achieve high performance forward linktransmission, and contribute to an increase in bandwidth capacity of amobile communication system, improvement in call quality, and areduction in transmission power of a mobile station.

[0141] While the invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the invention as definedby the appended claims.

What is claimed is:
 1. A transmission beam forming control apparatus ofa base station, for forming a transmission beam for a transmissionchannel signal to be transmitted to a mobile station from an antennaarray including a plurality of antenna elements, the apparatuscomprising: a transmission beam weight vector calculator for estimatinga direction of the mobile station by using a reception signal and areverse link power control bit received from the mobile station, andcalculating a transmission beam weight vector in the estimateddirection; and a transmission beam former for applying the calculatedtransmission beam weight vector to the transmission channel signal andproviding the applied transmission channel signal to the antenna array.2. The transmission beam forming control apparatus of claim 1, whereinthe transmission beam weight vector calculator comprises: a firstforward link covariance matrix calculator for calculating a forward linkcovariance matrix estimation value by using a signal received from themobile station via the antenna array, a reverse link power control valueof the mobile station, and a frame error rate; a second forward linkcovariance matrix calculator for calculating a forward link covariancematrix estimation value for other mobile stations; and an optimal weightvector calculator for calculating an optimal weight vector of thetransmission beam from the estimation values output from the first andsecond forward link covariance matrix calculators and the weight vectorfor the common channel signal.
 3. The transmission beam forming controlapparatus of claim 2, wherein the second forward link covariance matrixcalculator calculates the weight vector by considering an expectedaverage transmission power value for other mobile stations.
 4. Thetransmission beam forming control apparatus of claim 2, wherein thefirst forward link covariance matrix calculator comprises: a reverselink covariance matrix estimator for estimating a reverse linkcovariance matrix by using a signal received from the mobile station viathe antenna array and a reverse link power control signal; an AOA (Angleof Arrival) estimator for estimating an arrival angle of a signal fromthe reverse link covariance matrix value; a beamwidth estimator fordetermining a beamwidth of a forward link signal by using the reverselink covariance matrix value and the frame error rate; and a forwardlink covariance matrix synthesizer for synthesizing a forward linkcovariance matrix by using an output of the AOA estimator and an outputof the beamwidth estimator.
 5. The transmission beam forming controlapparatus of claim 2, wherein the optimal weight vector calculatorcalculates a transmission beam weight vector for maximizing asignal-to-interference plus noise ratio (SINR) for the forward link beamforming, the SINR being defined as${SINR} = \frac{P_{i}}{P_{q} + P_{\exp} + P_{oc}}$

where P_(i) represents in-phase component power for the common channelsignal, P_(q) represents quadrature-phase component power for the commonchannel signal, P_(exp) represents interference power due to thetransmission channel signal for other mobile stations located inside acell serviced by the base station, and P_(oc) represents interferencepower due to the transmission channel signal for other mobile stationslocated outside the cell.
 6. The transmission beam forming controlapparatus of claim 5, wherein the optimal weight vector calculatorcalculates a weight vector for the transmission beam in accordance withthe following equation $\begin{matrix}{{\underset{\_}{w}}_{m}^{opt} = {\gamma_{m}{\underset{\_}{w}}_{m}^{\prime}}} \\{{\underset{\_}{w}}_{m}^{\prime} = {\left( {{\sum\limits_{i = 1}^{M}R_{i}} + R_{oc}} \right)^{- 1}R_{m}{\underset{\_}{w}}_{p}}} \\{\gamma_{m} = {{\underset{\_}{w}}_{m}^{\prime}R_{m}{\underset{\_}{w}}_{p}}}\end{matrix}$

where ${\underset{\_}{w}}_{m}^{opt}$

represents an optimal weight vector of a transmission beam for themobile station, M represents the number of mobile stations currentlyserviced by the base station, R_(i) represents a transmission covariancematrix for an i^(th) mobile station among M mobile stations serviced bythe base station, R_(oc) represents an interference covariance matrixvalue for mobile stations serviced by other base stations, and w_(p)represents a common beam weight vector.
 7. The transmission beam formingcontrol apparatus of claim 2, wherein the optimal weight vectorcalculator calculates a transmission beam weight vector for maximizing asignal-to-interference plus noise ratio (SINR) for forward link beamforming, the SINR being defined as${SINR} = \frac{P_{d}}{P_{\exp} + P_{oc}}$

where P_(d) represents power of the transmission channel signal, P_(exp)represents interference power due to the transmission channel signal forother mobile stations located inside a cell serviced by the basestation, and P_(oc) represents interference power due to thetransmission channel signal for other mobile stations located outsidethe cell.
 8. The transmission beam forming control apparatus of claim 7,wherein a direction of the transmission beam weight vector formaximizing the SINR is calculated by${\underset{\_}{w}}_{m}^{opt} = {{Principal}\quad {Eigenvector}\quad {of}\quad \left( {{\sum\limits_{i = 1}^{M}R_{i}} + R_{oc}} \right)^{- 1}R_{m}}$

where ${\underset{\_}{w}}_{m}^{opt}$

represents an optimal weight vector of a transmission beam for themobile station, M represents the number of mobile stations currentlyserviced by the base station, R_(i) represents a transmission covariancematrix for an i^(th) mobile station among M mobile stations serviced bythe base station, R_(oc) and represents an interference covariancematrix value for mobile stations serviced by other base stations.
 9. Thetransmission beam forming control apparatus of claim 1, wherein abeamwidth of the transmission beam weight vector is determined accordingto a frame error rate (FER) during calculation of the transmission beamweight vector.
 10. The transmission beam forming control apparatus ofclaim 1, wherein the transmission beam weight vector calculatorminimizes phase mismatching between a common channel signal and thetransmission channel signal by dividing power of the transmissionchannel signal into an in-phase power component and a quadrature-phasepower component for the common channel signal, maximizing the in-phasepower component and minimizing the quadrature-phase power component. 11.The transmission beam forming control apparatus of claim 1, wherein thetransmission beam weight vector calculator calculates a transmissionbeam weight vector so as to minimize phase mismatching between thecommon channel signal and the transmission channel signal.
 12. Atransmission beam forming control method of a base station, for forminga transmission beam for a transmission channel signal to be transmittedto a mobile station from an antenna array including a plurality ofantenna elements, the method comprising the steps of: estimating adirection of the mobile station by using a reception signal and areverse link power control bit received from the mobile station, andcalculating a transmission beam weight vector in the estimateddirection; and applying the calculated transmission beam weight vectorto the transmission channel signal; and providing the appliedtransmission channel signal to the antenna array.
 13. The transmissionbeam forming control method of claim 12, wherein the transmission beamweight vector calculator calculates a transmission beam weight vector tominimize phase mismatching between a common channel signal and thetransmission channel signal. 14 The transmission beam forming controlmethod of claim 12, wherein the transmission beam weight vectorcalculation step comprises the steps of: calculating a first forwardlink covariance matrix estimation value by using a signal received fromthe mobile station via the antenna array, a reverse link power controlvalue of the mobile station, and a frame error rate; calculating asecond forward link covariance matrix estimation value for other mobilestations; and calculating an optimal weight vector of the transmissionbeam from the calculated first and second forward link covariance matrixestimation values and the weight vector for a common channel signal. 15.The transmission beam forming control method of claim 14, wherein thesecond forward link covariance matrix estimation value calculation stepcomprises the step of calculating the weight vector by considering anexpected average transmission power value for other mobile stations. 16.The transmission beam forming control method of claim 14, wherein thefirst forward link covariance matrix calculation step comprises thesteps of: estimating a reverse link covariance matrix by using a signalreceived from the mobile station via the antenna array and a reverselink power control signal; estimating an arrival angle of a signal fromthe reverse link covariance matrix value; determining a beamwidth of aforward link signal by using the reverse link covariance matrix valueand the frame error rate; and synthesizing a forward link covariancematrix by using the estimated arrival angle and the determinedbeamwidth.
 17. The transmission beam forming control method of claim 14,wherein the optimal weight vector calculation step comprises the step ofcalculating a transmission beam weight vector for maximizing asignal-to-interference plus noise ratio (SINR) for forward link beamforming, the SINR being defined as${SINR} = \frac{P_{i}}{P_{q} + P_{\exp} + P_{oc}}$

where P_(i) represents in-phase component power for the common channelsignal, P_(q) represents quadrature-phase component power for the commonchannel signal, P_(exp) represents interference power due to thetransmission channel signal for other mobile stations located inside acell serviced by the base station, and P_(oc) represents interferencepower due to the transmission channel signal for other mobile stationslocated outside the cell.
 18. The transmission beam forming controlmethod of claim 17, wherein the transmission beam weight vector formaximizing the SINR is calculated by $\begin{matrix}{{\underset{\_}{w}}_{m}^{opt} = {\gamma_{m}{\underset{\_}{w}}_{m}^{\prime}}} \\{{\underset{\_}{w}}_{m}^{\prime} = {\left( {{\sum\limits_{i = 1}^{M}R_{i}} + R_{oc}} \right)^{- 1}R_{m}{\underset{\_}{w}}_{p}}} \\{\gamma_{m} = {{\underset{\_}{w}}_{m}^{\prime}R_{m}{\underset{\_}{w}}_{p}}}\end{matrix}$

where ${\underset{\_}{w}}_{m}^{opt}$

represents an optimal weight vector of a transmission beam for themobile station, M represents the number of mobile stations currentlyserviced by the base station, R_(i) represents a transmission covariancematrix for an i^(th) mobile station among M mobile stations serviced bythe base station, R_(oc) represents an interference covariance matrixvalue for mobile stations serviced by other base stations, and w_(p)represents a common beam weight vector.
 19. The transmission beamforming control method of claim 14, wherein the optimal weight vectorcalculation step comprises the step of calculating a transmission beamweight vector for maximizing a signal-to-interference plus noise ratio(SINR) for forward link beam forming, the SINR being defined as${SINR} = \frac{P_{d}}{P_{\exp} + P_{oc}}$

where P_(d) represents power of the transmission channel signal, P_(exp)represents interference power due to the transmission channel signal forother mobile stations located inside a cell serviced by the basestation, and P_(oc) represents interference power due to thetransmission channel signal for other mobile stations located outsidethe cell.
 20. The transmission beam forming control method of claim 19,wherein a direction of the transmission beam weight vector formaximizing the SINR is calculated by${\underset{\_}{w}}_{m}^{opt} = {{Principal}\quad {Eigenvector}\quad {of}\quad \left( {{\sum\limits_{i = 1}^{M}R_{i}} + R_{oc}} \right)^{- 1}R_{m}}$

where ${\underset{\_}{w}}_{m}^{opt}$

represents an optimal weight vector of a transmission beam for themobile station, M represents the number of mobile stations currentlyserviced by the base station, represents a transmission covariancematrix for an i^(th) mobile station among M mobile stations serviced bythe base station, and R_(oc) represents an interference covariancematrix value for mobile stations serviced by other base stations. 21.The transmission beam forming control method of claim 12, wherein thetransmission beam weight vector calculation step comprises the step ofminimizing phase mismatching between a common channel signal and thetransmission channel signal by dividing power of the transmissionchannel signal into an in-phase power component and a quadrature-phasepower component for the common channel signal, maximizing the in-phasepower component and minimizing the quadrature-phase power component. 22.An apparatus for forming a transmission beam for a transmission channelsignal to be transmitted to each of mobile stations in a base stationapparatus including an antenna array having a plurality of antennaelements, the base station apparatus communicating with the mobilestations, the apparatus comprising: a reception beam former forseparating baseband signals received from the antenna elements accordingto mobile stations; a base station modem receiver for calculating andextracting a frame error rate and a forward link power control bit foreach mobile station from the signals received from the reception beamformer; a transmission beam controller for calculating a transmissionbeam weight vector and transmission beam power for minimizing phasemismatching between a common channel signal and the transmission channelsignal by using a separated baseband signal and an output of the basestation modem receiver; a transmission channel signal generator forgenerating data to be transmitted to each mobile station; and atransmission beam former for forming a transmission beam by applying thecalculated weight vector to an output of the transmission channel signalgenerator.
 23. The apparatus of claim 22, wherein the transmission beamcontroller comprises: a transmission beam weight vector calculator forcalculating the transmission beam weight vector for minimizing phasemismatching between the common channel signal and the transmissionchannel signal by using the separated baseband signal and an output ofthe base station modem receiver; and a transmission beam powercalculator for calculating the transmission beam power by using a powercontrol bit for each mobile station.
 24. The apparatus of claim 23,wherein the transmission beam weight vector calculator calculates atransmission beam weight vector for maximizing a signal-to-interferenceplus noise ratio (SINR) for forward link beam forming, the SINR beingdefined as ${SINR} = \frac{P_{i}}{P_{q} + P_{\exp} + P_{oc}}$

where P_(i) represents in-phase component power for the common channelsignal, P_(q) represents quadrature-phase component power for the commonchannel signal, P_(exp) represents interference power due to thetransmission channel signal for other mobile stations located inside acell serviced by the base station, and P_(oc) represents interferencepower due to the transmission channel signal for other mobile stationslocated outside the cell.
 25. The apparatus of claim 24, wherein thetransmission beam weight vector calculator calculates the weight vectorfor the transmission beam in accordance with the following equation$\begin{matrix}\begin{matrix}{{\underset{\_}{w}}_{m}^{opt} = {\gamma_{m}{\underset{\_}{w}}_{m}^{\prime}}} \\{{\underset{\_}{w}}_{m}^{\prime} = {\left( {{\sum\limits_{i = 1}^{M}\quad R_{i}} + R_{o\quad c}} \right)^{- 1}R_{m}{\underset{\_}{w}}_{p}}}\end{matrix} \\{\gamma_{m} = {{\underset{\_}{w}}_{m}^{\prime}R_{m}{\underset{\_}{w}}_{p}}}\end{matrix}$

where ${\underset{\_}{w}}_{m}^{opt}$

represents an optimal weight vector of a transmission beam for themobile station, M represents the number of mobile stations currentlyserviced by the base station, R_(i) represents a transmission covariancematrix for an i^(th) mobile station among M mobile stations serviced bythe base station, R_(oc) represents an interference covariance matrixvalue for mobile stations serviced by other base stations, and w_(p)represents a common beam weight vector.
 26. The apparatus of claim 24,wherein the transmission beam weight vector calculator calculates atransmission beam weight vector for maximizing a signal-to-interferenceplus noise ratio (SINR) for forward link beam forming, the SINR beingdefined as ${SINR} = \frac{P_{d}}{P_{e\quad {xp}} + P_{o\quad c}}$

where P_(d) represents power of the transmission channel signal, P_(exp)represents interference power due to the transmission channel signal forother mobile stations located inside a cell serviced by the basestation, and P_(oc) represents interference power due to thetransmission channel signal for other mobile stations located outsidethe cell.
 27. The apparatus of claim 26, wherein a direction of thetransmission beam weight vector for maximizing the SINR is calculated by${\underset{\_}{w}}_{m}^{opt} = {{{}_{{{Principal}\quad {Eigenvector}\quad {of}}\quad}^{}\left( {{\sum\limits_{i = 1}^{M}\quad R_{i}} + R_{o\quad c}} \right)_{}^{- 1}}R_{m}}$

where ${\underset{\_}{w}}_{m}^{opt}$

represents an optimal weight vector of a transmission beam for themobile station, M represents the number of mobile stations currentlyserviced by the base station, R_(i) represents a transmission covariancematrix for an i^(th) mobile station among M mobile stations serviced bythe base station, and R_(oc) represents an interference covariancematrix value for mobile stations serviced by other base stations.